Not always because of high blood pressure.
In my case, the veins in my nose are too close to the wall and when allergies kick in or when it is dry out they tend to crack and bleed.
I use to get them all the time when I was a kid. Rub some vasoline in your nostrils to keep them from cracking if it is dry in your neck of the woods.
All that said, however, if it continues and they do not stop easily, go to the doc.